Liquid crystal display device and image display method thereof

[0067] The first embodiment

[0068] Hereinafter, referring to the drawings, the liquid crystal display device according to the first embodiment of the present invention and an image display method used in the device will be described. FIG. 1 is a block diagram showing the overall configuration of the liquid crystal display device according to the first embodiment of the present invention. In FIG. 1, the video signal displayed on the liquid crystal panel 34 in the liquid crystal module unit 30 described later is supplied to the maximum gray scale detection unit 11 and the frame memory 13 in the video signal processing unit 10. As described later, the backlight device 35 is divided into a plurality of regions, and the liquid crystal panel 34 is divided into a plurality of regions corresponding to each region of the backlight device 35. For each region of the liquid crystal panel 34, the brightness (light intensity) of the backlight ) Are controlled separately.

[0069] figure 2 It is an example of the area division on the liquid crystal panel 34 and the backlight device 35, and is a perspective view schematically showing the correspondence between the area of ​​the liquid crystal panel 34 and the area of ​​the backlight device 35. Here, for easy understanding, the liquid crystal panel 34 and the backlight device 35 are separated from each other. Such as figure 2 As shown, the backlight device 35 is divided into regions 35a to 35d, and the regions 35a to 35d respectively have backlights. The liquid crystal panel 34 has, for example, a plurality of pixels composed of 1920 pixels in the horizontal direction and 1080 pixels in the vertical direction. The liquid crystal panel 34 having the plurality of pixels is divided into regions 34a to 34d corresponding to the regions 35a to 35d of the backlight device 35. In this example, the liquid crystal panel 34 is one-dimensionally divided into four regions 34a to 34d in the vertical direction, so one region contains 270 pixels in the vertical direction. Of course, there may be deviations in the number of pixels in the vertical direction among the four regions 34a to 34d.

[0070] The regions 34a to 34d on the liquid crystal panel 34 are not physically separated and divided, but a plurality of regions (regions 34a to 34d here) are set on the liquid crystal panel 34. In addition, the video signal supplied to the liquid crystal panel 34 corresponds to the plurality of regions set on the liquid crystal panel 34 and is processed as a video signal for each region displayed in the plurality of regions. In the plurality of areas set on the liquid crystal panel 34, the brightness of the backlight is individually controlled.

[0071] in figure 2 In the example shown, the liquid crystal panel 34 is divided into four areas in the vertical direction. Correspondingly, the backlight device 35 is divided into four areas in the vertical direction, but it can also be divided (differentiated) into more areas. area. In addition, as described later, the liquid crystal panel 34 may be divided into a plurality of regions in both the vertical direction and the horizontal direction, and correspondingly, the backlight device 35 may be divided into a plurality of regions in both the vertical direction and the horizontal direction. area. It is preferable that the number of regions to be divided (division) is large, and it is preferable to divide (division) in both the vertical direction and the horizontal direction rather than dividing (division) only in the vertical direction. Here, in order to simplify the description, figure 2 The four divisions shown in the vertical direction illustrate the action of FIG. 1.

[0072] Returning to FIG. 1, the maximum gray scale detection unit 11 detects the maximum gray scale of the video signal displayed on each area 34 a to 34 d of the liquid crystal panel 34 for each frame of the video signal. It is preferable to detect the maximum gray scale for each frame of the image signal, but it may be detected separately for every two frames according to the situation, and the maximum gray scale may be detected for each predetermined unit time. The data representing the maximum gradation of each region 34a to 34d detected by the maximum gradation detection section 11 is supplied to the image gain calculation section 12 in the image signal processing section 10 and the non-uniformization processing section 21 in the backlight brightness control section 20 . The video gain calculation unit 12 calculates the gain multiplied by the video signal displayed on the regions 34a to 34d as follows.

[0073] image 3 It is a diagram for explaining the calculation process of the gain obtained by the video gain calculation unit 12. The gain to be multiplied by the video signal is obtained for each video signal supplied to the respective regions 34a to 34d of the liquid crystal panel 34. Therefore, the calculation of the gain described below is performed on the respective video signals supplied to the regions 34a to 34d. In addition, in image 3 In the figure, the input signal (video signal) shown on the horizontal axis is 8 bits, indicating that the input signal takes a value of 0 to 255 in gray scale. In addition, the display brightness (display gradation) of the liquid crystal panel 34 shown on the vertical axis ignores the transmittance of the liquid crystal panel 34, and a value from 0 to 255 is used for the description for convenience. The number of bits of the video signal is not limited to 8 bits, and may be 10 bits, for example.

[0074] image 3 The curve Cv1 shown in (A) indicates the display brightness at which the input signal with a gray scale of 0 to 255 is displayed on the liquid crystal panel 34. The curve Cv1 is a curve in which y is represented by the 2.2 power to the 2.4 power of x when the horizontal axis is x and the vertical axis is y, and is a gamma curve generally called gamma 2.2 to 2.4. Depending on the type of LCD panel 34, there are image 3 (A) The case where the gamma curve Cv1 is different.

[0075] Here, as an example, such as image 3 As shown in (B), consider the case where the maximum gray scale of the input signal is 127, and the input signal takes a gray scale value of 0 to 127. The display brightness of the liquid crystal panel 34 at this time becomes a curve represented by the curve Cv2, and the display brightness takes a value of 0 to 56. At this time, it is considered that the backlight emits light at a gray scale of 255 of maximum brightness. The maximum brightness of the backlight refers to the brightness that the backlight should emit when the image signal is the maximum gray scale of 255 (that is, white). If image 3 The image signal represented by the curve Cv2 in (B) is multiplied by a gain of about 4.5, then it becomes image 3 (C) The curve Cv3 shown. The gain of about 4.5 is obtained from 255/56. in image 3 In the state (C), it is also considered that the backlight emits light at maximum brightness.

[0076] In this state, the image signal with the characteristic represented by the curve Cv3 does not have image 3 In (B), the original video signal with the characteristic represented by the curve Cv2, and the backlight consumes power unnecessarily. Therefore, if the brightness of the backlight is set to about 1/4.5 times the maximum brightness, as image 3 As shown in (D), a curve Cv3 with a display brightness of 0 to 255 becomes a curve Cv4 with a display brightness of 0 to 56. Accordingly, the video signal having the characteristic represented by the curve Cv4 is substantially equivalent to the original video signal having the characteristic represented by the curve Cv2, and the power consumption of the backlight is reduced.

[0077] That is, if the maximum gray scale in one frame period of the video signal displayed on the regions 34a to 34d is set to Gmax1, and the maximum gray scale obtained by the video signal determined by the number of bits of the video signal is set to Gmax0, the video gain The computing unit 12 uses Gmax0/Gmax1 for each of the regions 34a to 34d as a gain to be multiplied by the video signal displayed on the regions 34a to 34d. Gmax1/Gmax0, which is the reciprocal of the gain Gmax0/Gmax1, is used when the backlight brightness control unit 20 controls the brightness of the backlight. If the patterns of the image signals displayed on the areas 34a to 34d are different, the maximum gray scale Gmax1 of the areas 34a to 34d is of course different, so Gmax0/Gmax1 are different in the areas 34a to 34d. The structure and operation of the backlight brightness control unit 20 will be described in detail later.

[0078] In FIG. 1, the gain for each of the regions 34 a to 34 d obtained by the video gain calculation unit 12 is input to the multiplier 14. The multiplier 14 multiplies the video signals displayed on the areas 34a to 34d output from the frame memory 13 by respective gains and outputs them.

[0079] The video signal output from the multiplier 14 is supplied to the timing control unit 31 of the liquid crystal module unit 30. The liquid crystal panel 34 has the above-mentioned plurality of pixels 341, the data signal line driving part 32 is connected to the data signal line of the pixel 341, and the gate signal line driving part 33 is connected to the gate signal line. The video signal input to the timing control unit 31 is supplied to the data signal line driving unit 32. The timing control section 31 controls the timing of writing image signals into the liquid crystal panel 34 through the data signal line driving section 32 and the gate signal line driving section 33. The pixel data of each row constituting the image signal input to the data signal line drive unit 32 is sequentially written row by row to the pixels of each row by the gate signal line drive unit 33 driving the gate signal line. Thus, each frame of the video signal is sequentially displayed on the liquid crystal panel 34.

[0080] The backlight device 35 is arranged on the back side of the liquid crystal panel 34. As the backlight device 35, there are the following types: a direct type disposed directly under the liquid crystal panel 34; and a light guide plate type in which light emitted from the backlight is incident on the light guide plate to irradiate the liquid crystal panel 34. Any type may be used. The backlight device 35 is driven by the backlight driving unit 36. Power for causing the backlight to emit light is supplied from the power supply unit 40 to the backlight driving unit 36. In addition, power is supplied from the power supply unit 40 to each part of the circuit that requires power. The liquid crystal module unit 30 has a temperature sensor that detects the temperature of the backlight device 35 and a color sensor that detects the color temperature of light emitted from the backlight device 35.

[0081] Here, a specific configuration example of the backlight device 35 will be described. Figure 4 versus figure 2 Similarly, an example in which the backlight device 35 is divided into four areas in the vertical direction is shown. will Figure 4 The first configuration example of the backlight device 35 shown is called the backlight device 35A, which will be described later Figure 5 The second structural example of the backlight device 35 shown is called a backlight device 35B. In addition, the backlight device 35 is a collective term for the backlight devices 35A, 35B and other structural examples. Figure 4 (A) is a plan view of the backlight device 35A, Figure 4 (B) is a cross-sectional view showing a state where the backlight device 35A is cut in the vertical direction.

[0082] Such as Figure 4 As shown in (A) and (B), the backlight device 35A is a structure in which the light sources 352 of the backlight are arranged in a horizontal direction on a rectangular frame 351 having a predetermined depth. The light source 352 is, for example, an LED. The regions 35 a to 35 d are partitioned from each other by partition walls 353 that protrude from the bottom surface of the frame 351 at a predetermined height higher than the uppermost surface (top) of the light source 352. The inner side of the frame body 351 and the surface of the partition wall 353 are covered by a reflective sheet.

[0083] A diffuser plate 354 that diffuses light is attached to the upper part of the frame 351, and three optical sheets 355 are attached to the diffuser plate 354, for example. The optical sheets 355 are a combination of multiple sheets such as a diffusion sheet that diffuses light, a prism sheet (Prism Sheet), and a brightness enhancement film called DBEF (Dual Brightness Enhancement Film). Since the height of the partition wall 353 made of the reflective sheet does not reach the diffuser 354, the regions 35a to 35d are not completely separated and are not completely independent of each other. That is, in the backlight device 35A, the structure allows the light emitted from the light source 352 of each of the regions 35a to 35d to leak to other regions. As will be described in detail later, in the first embodiment, the amount of light leaking from each of the regions 35a to 35d to other regions is considered, and the brightness of the light emitted from the regions 35a to 35d is controlled.

[0084] Figure 5 It shows that when the liquid crystal panel 34 is divided into four regions in the vertical direction, and then divided into four regions in the horizontal direction, that is, when the liquid crystal panel 34 is two-dimensionally divided into 16 regions, it is used as the second structure of the backlight device 35 Example of the backlight device 35B. Figure 5 (A) is a plan view of the backlight device 35B, Figure 5 (B) is a cross-sectional view showing a state where the backlight device 35B is cut in the vertical direction, Figure 5 (C) is a cross-sectional view showing a state where the backlight device 35B is broken in the horizontal direction. here, Figure 5 (B) means to Figure 5 (A) The column of the left end area is truncated, Figure 5 (C) means to Figure 5 (A) The state where the line of the upper end region is cut off. In addition, in Figure 5 In, and Figure 4 The same parts are marked with the same reference numerals, and their descriptions are appropriately omitted.

[0085] The frame 351 is divided into 16 regions of regions 35a1 to 35a4, 35b1 to 35b4, 35c1 to 35c4, and 35d1 to 35d4 by dividing walls 353 in the horizontal and vertical directions. In the backlight device 35B, the light emitted from the light sources 352 of the regions 35a1 to 35a4, 35b1 to 35b4, 35c1 to 35c4, and 35d1 to 35d4 are also allowed to leak to other regions. In the first embodiment, considering the amount of light leaking from the respective regions 35a1 to 35a4, 35b1 to 35b4, 35c1 to 35c4, 35d1 to 35d4 to other regions, the amount of light from the regions 35a1 to 35a4, 35b1 to 35b4, 35c1 to 35c4, 35d1 to The brightness of the light emitted by the 35d4 is controlled.

[0086] LED is a light source with high directivity. Therefore, when the LED is used as the light source 352, the partition wall 353 covered by the reflective sheet can be more Figure 4 , Figure 5 The stated status is low and can be removed depending on the situation. By covering the elements of the light source 352 with a dome-shaped lens, the same effect as the provision of the partition wall 353 can be obtained. As the light source of the backlight, a light source other than LED may be used, and other light sources such as CCFL or external electrode fluorescent lamp (EEFL) may also be used. However, the LED is easy to control the emission brightness and the emission area, and therefore, as the light source 352 used in the first embodiment, an LED is preferable. The specific structure of the backlight device 35 is not limited to Figure 4 or Figure 5 The structure shown.

[0087] Figure 4 , Figure 5 The illustrated light source 352 is specifically configured as follows. Figure 6 In the first configuration example of the light source 352 shown in (A), the G LED 357G, the R LED 357R, the B LED 357B, and the G LED 357G are mounted on a substrate 356 in this order. The substrate 356 is, for example, an aluminum substrate or a glass epoxy substrate. Figure 4 , Figure 5 The illustrated light source 352 is equivalent to making multiple Figure 6 The light sources 352 of (A) are arranged in a row. Figure 6 In the second configuration example of the light source 352 shown in (B), the R LED 357R, the G LED 357G, the B LED 357B, and the G LED 357G are mounted in a diamond shape on a substrate 356. Figure 4 , Figure 5 The illustrated light source 352 is equivalent to making multiple Figure 6 The light sources 352 of (B) are arranged in a row.

[0088] Figure 6 In the third configuration example of the light source 352 shown in (C), 12 LED chips 358 integrally provided with R LEDs 357R, G LEDs 357G, and B LEDs 357B are mounted on a substrate 356. Figure 4 , Figure 5 The illustrated light source 352 is equivalent to making multiple Figure 6 The light sources 352 of (C) are arranged in a row. Figure 6 In the fourth configuration example of the light source 352 shown in (D), two white (W) LEDs 357W are mounted on a substrate 356. Figure 4 , Figure 5 The illustrated light source 352 is equivalent to making multiple Figure 6 The light sources 352 of (D) are arranged in a row. In addition, as the LED 357W, there are the following types: the yellow phosphor is excited by the light emitted from the LED of B to obtain white light; and the ultraviolet light emitted from the LED is used to excite the phosphors of R, G, and B to obtain white light. Is any of them.

[0089] Next, returning to FIG. 1, the structure and operation of the backlight brightness control unit 20 will be described. The backlight brightness control unit 20 has a light emission brightness calculation unit 22, a white balance adjustment unit 23, and a PWM timing generation unit 24 in addition to the non-uniformization processing unit 21. Here also for the sake of simplicity, with Figure 4 The illustrated backlight device 35A will be described as the backlight device 35. If the maximum brightness of the backlight is set to Bmax, the brightness that the respective backlights of the regions 35a to 35d of the backlight device 35 should emit is the maximum brightness Bmax multiplied by Gmax1/Gmax0 obtained for each of the regions 34a to 34d. In this way, the non-uniformization processing unit 21 obtains the brightness B that the backlight of the regions 35a to 35d should emit 1 ~B 4.

[0090] The calculated luminous brightness B 1 ~B 4 It is not the brightness directly above the light source 352 when the light source 352 as the backlight emits light, but the brightness of the light emitted from the backlight device 35. That is, in Figure 4 , Figure 5 In the structure example, the luminous brightness B 1 ~B 4 It is the brightness above the optical sheet 355. In addition, the calculated light emission brightness that should be emitted from one area of ​​the backlight device 35 is collectively referred to as B. In the following description, it is assumed that the brightness distribution of light emitted from the regions 35a to 35d of the backlight device is substantially the same in each region, but there are cases where the brightness distribution is different in one region. At this time, the brightness at any point in an area is the luminous brightness B 1 ~B 4 That's it.

[0091] Conventionally, if all the video signals in the regions 34a to 34d have the same gray scale, the light emission brightness B of the regions 35a to 35d is 1 ~B 4 All the same. That is, at this time, the calculated luminous brightness B 1 ~B 4 It is directly used as the actual luminous brightness. In contrast, in the first embodiment, the non-uniformization processing unit 21 calculates the calculated emission brightness B 1 ~B 4 Multiplied by the non-uniformization coefficient p 1 ~p 4 , The brightness of the light actually emitted from the regions 35a to 35d becomes p 1 B 1 , P 2 B 2 , P 3 B 3 , P 4 B 4. Coefficient p 1 ~p 4 It is a value greater than 0 and less than 1. The inventors found that when the backlight is made to emit light at a light emission brightness slightly lower than the calculated light emission brightness at the periphery of the screen, compared with directly emitting the calculated light emission brightness on the entire screen of the liquid crystal panel 34, the liquid crystal panel 34 The quality of the image displayed on the screen is improved.

[0092] Therefore, in one-dimensional division of the area of ​​the backlight device 35 into four Figure 4 In the example, it is preferable to set the light emission luminance B from the areas 35a and 35d corresponding to the upper and lower ends of the screen in the areas 35a to 35d. 1 , B 4 Brighter than the luminous brightness B from areas 35b and 35c 2 , B 3 low. Specifically, as an example, let p 1 Set to 0.8, set p 2 , P 3 Set to 1, set p 4 Set to 0.8.

[0093] In the full white state where the entire liquid crystal panel 34 displays white, if the brightness of the areas 34b and 34c of the liquid crystal panel 34 is 500 [cd/m 2 ], then 400[cd/m 2 ]. Therefore, the power consumption in the regions 35a and 35d of the backlight device 35 can be reduced by 20%. In this way, in the first embodiment, by providing the non-uniformization processing unit 21, the quality of the image displayed on the liquid crystal panel 34 is not reduced, but the quality is improved, and the power consumption of the backlight device 35 can be reduced. Considering both the image quality and the reduction of power consumption, the coefficient p 1 ~p 4 Preferably it is 0.8 or more and 1.0 or less. That is, the coefficient p multiplied by the light emission brightness of the backlight is set to 1 in the center of the screen, and the coefficient p multiplied by the light emission brightness is set in the range up to the lower limit of 0.8 in the peripheral portion of the screen.

[0094] Furthermore, the non-uniformization coefficient p when the liquid crystal panel 34 and the backlight device 35 are divided into two-dimensional regions will be described. Here, the case of dividing into eight regions in both the horizontal direction and the vertical direction is taken as an example, that is, the case of dividing into 64 regions in two dimensions as an example. Such as Figure 7 As shown, the areas of the backlight device 35 at this time are 35a1 to 35a8, 35b1 to 35b8, 35c1 to 35c8, 35d1 to 35d8, 35e1 to 35e8, 35f1 to 35f8, 35g1 to 35g8, 35h1 to 35h8. Although not shown in particular, the liquid crystal panel 34 is divided into 64 areas corresponding to the 64 areas of the backlight device 35.

[0095] Figure 8 (A) is multiplied by the calculated luminous brightness of each of the 8 horizontal areas on the four-row areas 35c1 to 35c8, 35d1 to 35d8, 35e1 to 35e8, and 35f1 to 35f8 in the vertical direction of the backlight device 35 An example of the coefficient p. Figure 8 The left-right direction of (A) is the horizontal position, the left side is the left end of the screen, and the right side is the right end of the screen. In this example, the coefficient p is set to 1 for the four regions that are the central portion in the horizontal direction, the coefficient p is set to 0.9 for the regions located on the left and right, and the coefficient p is set to 0.8 for the regions at the left and right end portions.

[0096] It is preferable that the coefficient p gradually decreases in a stepwise manner as it approaches the left and right ends of the screen from the center portion where the coefficient p is 1. In this case, it is preferable that the coefficient p is bilaterally symmetrical. Here, although the coefficients p on the four areas of the central part are set to 1, the coefficients p on the two areas of the central part may be set to 1, starting from the areas on the left and right of the two areas to the left and right. As far as the end region, the coefficient p is sequentially decreased in a range from a value less than 1 to 0.8. In addition, when the number of divisions is an odd number, there may be only one area in the horizontal direction where the coefficient p is 1. The horizontal characteristics of the coefficient p can be appropriately set to produce the most ideal image quality on the actual screen.

[0097] Figure 8 (B) is multiplied by the calculated luminous brightness of each of the eight vertical regions in the four columns of regions 35a3 to 35h3, 35a4 to 35h4, 35a5 to 35h5, and 35a6 to 35h6 in the horizontal direction of the backlight device 35 An example of the coefficient p. Figure 8 The left-right direction of (B) is the position in the vertical direction, the left side is the upper end of the screen, and the right side is the lower end of the screen. In this example, the coefficient p is set to 1 for the four regions that are the central portion in the vertical direction, the coefficient p is set to 0.9 for the regions located above and below, and the coefficient p is set to 0.8 for the regions at the upper and lower ends.

[0098] In the vertical direction, it is also preferable that the coefficient p gradually decreases stepwise as it approaches the upper and lower ends of the screen from the center where the coefficient p is 1. In this case, the coefficient p is preferably symmetrical up and down. Here, although the coefficients p on the four areas of the central part are set to 1, the coefficients p on the two areas of the central part may be set to 1, starting from the upper and lower areas of the two areas to the upper and lower areas. As far as the end region, the coefficient p is sequentially decreased in a range from a value less than 1 to 0.8. In addition, when the number of divisions is an odd number, there may be only one area in the vertical direction where the coefficient p is 1. The characteristics of the coefficient p in the vertical direction can be appropriately set to produce the most ideal image quality on the actual screen. In addition, the characteristics in the horizontal direction and the characteristics in the vertical direction of the coefficient p may be different.

[0099] In this way, from the non-uniformization processing unit 21 in FIG. 1, data indicating the emission luminance of light that should actually be emitted from each area of ​​the backlight device 35 is obtained. The coefficient p used in the non-uniformization processing unit 21 is supplied from the control unit 50. The control unit 50 can be constituted by a microcomputer, and the coefficient p can be changed arbitrarily. The data representing the emission brightness is input to the emission brightness calculation unit 22, and the brightness of the light to be emitted by each light source 352 is calculated as follows. First, the backlight device 35 is a backlight device 35A having regions 35a to 35d, and the light emission brightness of the light that should actually be emitted from the regions 35a to 35d is p 1 B 1 , P 2 B 2 , P 3 B 3 , P 4 B 4 The calculation method of the brightness of the light that the light source 352 should emit at the time will be described.

[0100] Picture 9 (A) is to Figure 4 In the state where the cross-sectional view of (B) is turned horizontally, the optical sheets 355 are omitted here. The luminous brightness of light from regions 35a to 35d is p 1 B 1 , P 2 B 2 , P 3 B 3 , P 4 B 4 , And let p 1 B 1 =B 1 ′, p 2 B 2 =B 2 ′, p 3 B 3 =B 3 ′, p 4 B 4 =B 4 '. The luminous brightness B'marked with """ refers to the luminous brightness that has been non-uniformized by the non-uniformization processing unit 21, and the luminous brightness B not marked "" refers to the luminous brightness that has not been non-uniformized. . When the light source 352 of each of the regions 35a to 35d emits light alone, the light emission brightness directly above the light source 352 is set to Bo 1 , Bo 2 , Bo 3 , Bo 4. As described above, the light emitted from the respective light sources 352 in the regions 35a to 35d is allowed to leak to other regions, so B 1 ′, B 2 ′, B 3 ′, B 4 ′It is not related to the luminous brightness Bo 1 , Bo 2 , Bo 3 , Bo 4 the same. In addition, the attenuation of light caused by the diffuser 354 or the optical sheets 355 is very weak, and it is not considered. In addition, the light emission brightness directly above the light source 352 when the light source 352 in one area of ​​the backlight device 35 emits light alone is collectively referred to as Bo.

[0101] Such as Picture 9 As shown in (A), when all the light sources 352 in the regions 35a to 35d emit light, the light emitted from each light source 352 becomes the emission brightness Bo 1 , Bo 2 , Bo 3 , Bo 4 K times the light leakage L 1 Leakage to adjacent areas. k is the attenuation coefficient when light leaks, and is a value greater than 0 and less than 1. The light leakage to other areas other than the light-emitting area is further analyzed. Picture 9 (B) shows a state where light is leaked to the regions 35b to 35d when only the light source 352 of the region 35a emits light. From the light source 352 in the area 35a, the luminous brightness Bo 1 The emitted light becomes the brightness k Bo1 Light leakage L 1 , Leaks out to area 35b. Brightness k Bo 1 Light leakage L 1 Further becomes k times the light leakage, so it becomes k 2 Bo 1 Light leakage L 2 , Leaking to area 35c. Brightness k 2 Bo 1 Light leakage L 2 Further becomes k times the light leakage, so it becomes k 3 Bo 1 Light leakage L 3 , Leaking to area 35d.

[0102] At that Picture 9 In the case of (B), the emission brightness Bo is roughly emitted from the area 35a 1 The light. Passing brightness k Bo from area 35b 1 Light leakage L 1 Emitting, passing brightness k from area 35c 2 Bo 1 Light leakage L 2 Luminous, passing brightness k from area 35d 3 Bo 1 Light leakage L 3 Glow.

[0103] When the light sources 352 in the areas 35a to 35d are individually lit, the brightness of the light emitted from the areas 35a to 35d is as follows Picture 10 Shown. When all the light sources 352 in the areas 35a to 35d are lit, the brightness of the light emitted from each area 35a to 35d is Picture 10 The luminance shown in the table is the sum total of all the luminances in the vertical direction. That is, the brightness of the light emitted from the area 35a is Bo 1 +kBo 2 +k 2 Bo 3 +k 3 Bo 4 , The brightness of the light emitted from the area 35b is k Bo 1 +Bo 2 +k Bo 3 +k 2 Bo 4. The brightness of the light emitted from area 35c is k 2 Bo 1 +k Bo 2 +Bo 3 +k Bo 4 , The brightness of the light emitted from area 35d is k 3 Bo 1 +k 2 Bo 2 +k Bo 3 +Bo 4. The luminous brightness of the light that should be emitted from the areas 35a to 35d is B 1 ′~B 4 ′, it can be seen that Bo 1 +k Bo 2 +k 2 Bo 3 +k 3 Bo 4 Set to B 1 ′, set k Bo in area 35b 1 +Bo 2 +k Bo 3 +k 2 Bo 4 Set to B 2 ′, in the area 35c, k 2 Bo 1 +k Bo 2 +Bo 3 +k Bo 4 Set to B 3 ′, in the area 35d, k 3 Bo 1 +k 2 Bo 2 +k Bo 3 +Bo 4 Set to B 4 '.

[0104] Picture 11 The formula (1) shown in (A) will be used for the emission brightness Bo of the light emitted from the light source 352 1 , Bo 2 , Bo 3 , Bo 4 Get luminous brightness B 1 ′, B 2 ′, B 3 ′, B 4 The conversion formula of ′ is expressed by a matrix operation formula. Picture 11 The formula (2) shown in (B) will be used from the luminous brightness B 1 ′, B 2 ′, B 3 ′, B 4 ′Get the luminous brightness Bo 1 , Bo 2 , Bo 3 , Bo 4 The conversion formula of is expressed by matrix operation. Picture 11 In the formula (3) shown in (C), the formula (2) is organized in order to facilitate calculation on the circuit in the emission luminance calculation section 22. Picture 11 The formula (4) shown in (D) represents the constants a, b, and c of the formula (3). From Picture 11 The formula (3) of (C) shows that the luminous brightness Bo 1 , Bo 2 , Bo 3 , Bo 4 , The light emission brightness B can be multiplied by a coefficient (conversion coefficient) based on the amount of light leaked from the light source 352 of the regions 35a to 35d to other regions other than the own region 1 ′, B 2 ′, B 3 ′, B 4 'Come to get it.

[0105] Since light leakage L from one area of ​​the backlight device 35 to an adjacent area can be measured 1 ,Thus, in Picture 9 , Picture 10 The value of the attenuation coefficient k described in can be obtained in advance. Therefore, according to Picture 11 (C) formula (3) and Picture 11 The formula (4) of (D) correctly calculates the luminous brightness Bo of the light that should be emitted by the light source 352 of each of the regions 35a to 35d 1 , Bo 2 , Bo 3 , Bo 4.

[0106] In addition, when the attenuation coefficient k of light leakage to the adjacent area is small, the term of k to the second power or more is reduced to a negligible degree. At this time, it can also be assumed that the light emitted from one area only leaks to the adjacent area, and approximate calculations can be performed. That is, it is also possible to calculate a term of k to the second power or more as 0. In addition, depending on the structure of the backlight device 35, there is also light emitted from one area that is different from k 2 Times,...,k n Times (here n=3) different attenuation methods leak, but the light leakage to each area can be measured in advance, so in this case, the luminous brightness Bo of the light that the light source 352 should emit can also be accurately calculated 1 , Bo 2 , Bo 3 , Bo 4. This is different in the area segmentation method Figure 5 or Figure 7 The same applies to the situation.

[0107] In addition, when the backlight device 35 is divided into 8 areas in the vertical direction, if the light emission brightness of the light that should be emitted from the 8 areas is B 1 ′~B 8 ′, the luminous brightness directly above the light source 352 when the light source 352 on the 8 areas emits light alone is set to Bo 1 ~Bo 8 , Then the luminous brightness Bo 1 ~Bo 8 Can be based on Picture 12 The formula (5) shown is calculated. Furthermore, if it is generalized as being divided into n regions in the vertical direction (n is an integer greater than or equal to 2), the light emission brightness B 1 ′~B n 'use Figure 13 The formula (6) shown in (A) is obtained, the luminous brightness Bo 1 ~Bo n , Can be based on Figure 13 The formula (7) shown in (B) is calculated.

[0108] Next, the backlight device 35 is Figure 5 The calculation method of the brightness of the light that the light source 352 should emit when the backlight device 35B is shown will be described. Such as Figure 14 As shown, it is assumed that the light leakage from the light source 352 of the regions 35a1 to 35a4, 35b1 to 35b4, 35c1 to 35c4, and 35d1 to 35d4 of the backlight device 35B to adjacent regions in the horizontal direction is m times the light emitted from the light source 352. The attenuation coefficient m in the horizontal direction is a value greater than 0 and less than 1. The light leakage to the area adjacent in the vertical direction is k times the light emitted from the light source 352 as in the case of the backlight device 35A. Let the light emission brightness of the light that should actually be emitted from the regions 35a1 to 35a4, 35b1 to 35b4, 35c1 to 35c4, and 35d1 to 35d4 of the backlight device 35B be B 11 ′~B 14 ′, B 21 ′~B 24 ′, B 31 ′~B 34 ′, B 41 ′~B 44 '. In order to obtain the luminous brightness B 11 ′~B 14 ′, B 21 ′~B 24 ′, B 31 ′~B 34 ′, B 41 ′~B 44 ′, the luminous brightness of the light that should be emitted by the light source 352 in each area is set to Bo 11 ~Bo 14 , Bo 21 ~Bo 24 , Bo 31 ~Bo 34 , Bo 41 ~Bo 44.

[0109] If will be Picture 9 , Picture 10 The calculation method of luminous brightness in consideration of light leakage described in is also applicable to the horizontal direction, and the matrix calculation formula is shown in FIG. 15. The formula (8) shown in FIG. 15(A) is used for the emission brightness Bo of the light emitted from the light source 352 11 ~Bo 44 Get luminous brightness B 11 ′~B 44 The conversion formula of the matrix operation formula. The formula (9) shown in Figure 15(B) is used to obtain the brightness B 11 ′~B 44 ′Get the luminous brightness Bo 11 ~Bo 44 The conversion formula of the matrix expression. If formula (9) is organized, it becomes formula (10) shown in FIG. 15(C). The formula (11) shown in FIG. 15(D) represents the constants a, b, c, d, e, and f of the formula (10). in Figure 14 In the case of, the values ​​of the attenuation coefficients k and m can also be obtained in advance. Therefore, the areas 35a1 to 35d4 can be correctly calculated according to the formula (10) in Fig. 15(C) and the formula (11) in Fig. 15(D) The luminous brightness Bo of the light that the respective light source 352 should emit 11 ~Bo 44.

[0110] When the backlight device 35 is divided into 8 areas in both the horizontal direction and the vertical direction, if the light emission brightness of the light emitted from the 64 areas is B 11 ′~B 88 ′, the luminous brightness directly above the light source 352 when the light source 352 on the 64 areas emits light alone is set to Bo 11 ~Bo 88 , Then the luminous brightness B 11 ′~B 88 ′Using formula (12) shown in Figure 16(A), the luminous brightness Bo 11 ~Bo 88 It can be calculated according to formula (13) shown in Fig. 16(B). Furthermore, if generalized as being divided into n regions (n ​​is an integer greater than or equal to 2) in both the horizontal direction and the vertical direction, the emission brightness Bo 11 ~Bo n，n Can use luminous brightness B 11 ′~B n，n ′ Is calculated according to formula (14) shown in Fig. 17. Although the illustration is omitted, it is divided into nh regions in the horizontal direction (nh is an integer greater than or equal to 2) and nv regions in the vertical direction (nv is an integer greater than or equal to 2 and has a different value from nh) In the case of, it is also possible to accurately calculate the luminous brightness of the light that each light source 352 should emit by using a matrix calculation formula.

[0111] Returning to FIG. 1, the attenuation coefficients k and m used in the emission luminance calculation unit 22 are supplied from the control unit 50. The attenuation coefficients k and m can be changed arbitrarily. The data indicating the emission luminance of light to be emitted by each light source 352 in the plurality of regions of the backlight device 35 obtained as described above is supplied to the white balance adjustment unit 23. The white balance adjustment unit 23 is input with temperature data indicating the temperature of the backlight device 35 output from the temperature sensor 37 and color temperature data indicating the color temperature of the light emitted from the backlight device 35 output from the color sensor 38.

[0112] As described above, if the temperature of the backlight device 35 changes, the brightness of the light emitted from the LED (especially the R LED) changes. Therefore, when the light source 352 is a three-color LED, the white balance adjustment unit 23 adjusts the light intensity of the R, G, and B LEDs based on the temperature data and the color temperature data to adjust to the optimal white balance. In addition, the white balance of the backlight device 35 may be adjusted based on the external control signal Sct1 supplied from the control unit 50. In addition, when the change in the white balance of the backlight caused by the temperature change of the light source 352 or the change after a long time is small, the white balance adjustment unit 23 may be eliminated.

[0113] The data representing the emission brightness of light to be emitted by each light source 352 on the plurality of regions of the backlight device 35 output from the white balance adjustment unit 23 is supplied to the PWM timing generation unit 24. When the light source 352 is an LED, the light emission of the LEDs of various colors is controlled according to a pulse width modulation signal whose pulse width is modulated, for example. The PWM timing generating unit 24 supplies PWM timing data including the timing of generating the pulse width modulation signal and the pulse width for adjusting the amount of light emission (lighting time) to the backlight driving unit 36. The backlight driving unit 36 ​​generates a driving signal as a pulse width modulation signal based on the input PWM timing data, and drives the light source 352 (LED) of the backlight device 35.

[0114] Here, an example is shown in which the LED is driven by a pulse width modulation signal, but the light-emitting brightness of the LED can also be controlled by adjusting the value of the current flowing through the LED. At this time, a timing generating unit that generates timing data for determining the timing and current value of the current flowing through the LED may be provided instead of the PWM timing generating unit 24. In addition, when the light source 352 is a light source other than an LED, the amount of light emission can be controlled according to the type of light source, and a timing generation unit that generates timing data corresponding to the type of light source can be used.

[0115] In FIG. 1, the backlight brightness control section 20 is independent of the control section 50, but the control section 50 may provide all or part of the circuits in the backlight brightness control section 20. In addition, in the configuration of FIG. 1, for example, the maximum gradation detection unit 11, the image gain calculation unit 12, and the backlight brightness control unit 20 may be configured by hardware, software, or a mixture of the two. Needless to say, the display of each frame of the video signal output from the video signal processing unit 10 on the liquid crystal panel 34 and the control of the backlight brightness corresponding to the maximum brightness of the video signal of each frame by the backlight brightness control unit 20 are synchronized with each other. The illustration of the structure for synchronizing the two is omitted in FIG. 1.

[0116] use Figure 18 The operation of the liquid crystal display device shown in FIG. 1 described above and the steps of the image display method performed in the liquid crystal display device shown in FIG. 1 will be described separately. in Figure 18 In step S11, the maximum gray scale detection unit 11 detects the maximum gray scale of the video signal for each of the plurality of areas of the liquid crystal panel 34. In step S12, the image gain calculation unit 12 calculates a gain that is multiplied by the image signal displayed on each area of ​​the liquid crystal panel 34. In step S13, the liquid crystal module 30 displays the image signal of each area multiplied by the gain on the liquid crystal panel 34. Steps S14 to S17 are executed in parallel with these steps S12 and S13.

[0117] In step S14, the non-uniformization processing unit 21 obtains the emission brightness B of the light that should be emitted from the plurality of regions of the backlight device 35, and in step S15, the emission brightness B is multiplied by the coefficient p as the emission brightness B', The brightness of a plurality of areas of the liquid crystal panel 34 becomes uneven. In step S16, the light emission luminance calculation unit 22 obtains the light emission luminance Bo of the light to be emitted by the light source 352 itself in the plurality of regions of the backlight device 35 based on the calculation formula using the light emission luminance B′ and the conversion coefficient. In addition, in step S17, the PWM timing generating unit 24 and the backlight driving unit 36 ​​cause the light sources 352 of the plurality of regions of the backlight device 35 to emit light with the emission luminance Bo in a state synchronized with step S13.

[0118] In the structure shown in FIG. 1, the emission brightness B′ subjected to the non-uniformization processing by the non-uniformization processing section 21 is obtained, and the emission brightness calculation section 22 obtains the emission brightness Bo based on the emission brightness B′, but it may be After the emission brightness Bo is obtained by the emission brightness calculation unit 22, non-uniformization processing is performed. That is, the non-uniformization processing unit 21 and the emission luminance calculation unit 22 may be exchanged. The operation and procedure at this time will be described using FIG. 19.

[0119] In Fig. 19, steps S21~S23 and Figure 18 The steps S11 to S13 are the same. In step S24, the emission brightness control unit 22 obtains the emission brightness B of the light that should be emitted from a plurality of areas of the backlight device 35, and in step S26, obtains the backlight based on the calculation formula using the emission brightness B and the conversion coefficient. The luminous brightness Bo of the light that the light source 352 in the multiple regions of the device 35 should emit. In step S25, the non-uniformization processing unit 21 multiplies the emission luminance Bo by the coefficient p as the emission luminance Bo'. In addition, in step S27, the PWM timing generating unit 24 and the backlight driving unit 36 ​​cause the light sources 352 of the plurality of regions of the backlight device 35 to emit light with the emission luminance Bo' in a state synchronized with step S23.

[0120] However, the non-uniformization processing of the non-uniformization processing section 21 is necessary when it is desired to reduce the power consumption of the backlight device 35 further than the structure described in the non-patent document 1 or the above-mentioned patent documents 1 to 3. When the power consumption may be the same as the configuration described in these documents, the non-uniformization processing unit 21 may be omitted. use Picture 20 The operation and procedure at this time will be described. in Picture 20 In the steps S31 to S33 and Figure 18 The steps S11 to S13 are the same. In step S34, the emission luminance calculation unit 22 obtains the emission luminance B of the light to be emitted from a plurality of areas of the backlight device 35, and in step S36, obtains the backlight device based on the calculation formula using the emission luminance B and the conversion coefficient The light emission brightness Bo of the light that the light source 352 itself should emit in the multiple areas of 35. In addition, in step S37, the PWM timing generating unit 24 and the backlight driving unit 36 ​​cause the light sources 352 of the plurality of regions of the backlight device 35 to emit light with the emission luminance Bo in a state synchronized with step S33.

[0121] As described above, in the liquid crystal display device according to the first embodiment, the backlight device 35 has a structure that allows the light emitted from the respective light sources 352 of the plurality of areas to leak to other areas other than its own area. Therefore, it is not necessary to connect the liquid crystal panel 34 and The area of ​​the backlight device 35 corresponds with high accuracy. In addition, it is possible to accurately calculate the light emission brightness B that should be emitted from each of the multiple areas of the backlight device 35 based on the light emission brightness Bo of the light source 352 itself when the light source 352 of each area is made to emit light individually. Therefore, the brightness of the backlight irradiated on a plurality of areas on the liquid crystal panel 34 can be accurately controlled according to the brightness of the image signal displayed on the area.

[0122] Furthermore, each area of ​​the backlight device 35 is not completely independent, and the light emission brightness Bo is obtained using an arithmetic equation that takes into account the structure of the light emitted from the light source 352 leaking to other areas other than its own area. The brightness or hue in the area is not prone to deviation, and the quality of the image displayed on the liquid crystal panel 34 can be improved.

[0123] Second embodiment

[0124] FIG. 21 is a block diagram showing the overall configuration of a liquid crystal display device according to a second embodiment of the present invention. In FIG. 21, the same parts as those in FIG. 1 are denoted by the same reference numerals, and their descriptions are appropriately omitted. In addition, in FIG. 21, the non-uniformization processing part 21 in FIG. 1 is omitted for simplification, but it may be a structure having the non-uniformization processing part 21 as in the first embodiment.

[0125] As described above, in the first embodiment, the light emission luminance Bo of the light that should be emitted by the light source 352 itself in the multiple areas of the backlight device 35 is obtained from the light emission luminance calculation unit 22, and the light sources 352 in the multiple areas emit light. The emission brightness Bo is the brightness value at the center point of each area. Figure 22 (A) means that only the backlight device 35 such as Figure 4 (A) shows the brightness distribution when the area 35b in the backlight device 35A divided into four areas in the vertical direction emits light. In area 35b Figure 22 (A) Luminous brightness Bo shown 2 When emitting light, the luminous brightness in areas 35a and 35c is k Bo 2 , The luminous brightness in area 35d is k 2 Bo 2 , Becomes the brightness distribution shown in the figure. The amount of light emitted from the light source 352 in the area 35b at this time can be expressed as Figure 22 (B) The hatched area in (B). which is, Figure 22 The amount of light shown in (B) can be expressed as Figure 22 The brightness distribution of (A) represents the integral value of light (light beam) in the range.

[0126] It is preferable to obtain the light emission luminance B of light to be emitted from a plurality of areas from the light emission luminance Bo of the light from the light source 352 itself from each area, and it is preferable to obtain it from the light emission amount as the integral value of the light emitted from the light source 352. Therefore, in the second embodiment shown in FIG. 21, between the light emission luminance calculation unit 22 and the white balance adjustment unit 23, there is provided a light emission amount calculation unit 25 that converts the light emission brightness Bo into the light emission amount Boig as an integrated value. . The amount of luminescence Boig can be easily obtained from the calculation formula that converts the luminous intensity Bo to the luminous amount Boig.

[0127] Figure 23 (A) is an arithmetic expression taking the case of the backlight device 35A as an example.Figure 23 (B) Yes Figure 23 The constant s in formula (15) shown in (A) 1 ~s 4 , The constant s 1 ~s 4 The attenuation coefficient k can be expressed as formula (16). In addition, Figure 23 (A) and (B) Approximate formulas are used to express calculation formulas for converting the luminous brightness Bo to the luminous amount Boig. For example, when the area 35a in the backlight device 35A emits light, the integral value of the light irradiated on the liquid crystal panel 34 can be approximated by Figure 24 The formula (17) shown indicates that k 3 The term of is very small, so if it is ignored, it can be expressed by formula (18). In addition, when the region 35b in the backlight device 35A emits light, the integral value of the light irradiated on the liquid crystal panel 34 can be approximately expressed by the formula (19), and if the formula (19) is rewritten, it becomes the formula (20). When the backlight device 35 is divided into a plurality of regions in the vertical direction, the coefficient s multiplied by the emission brightness Bo of the regions located at the upper and lower ends is 1+k, which is equal to the coefficient s of each region sandwiched between the upper and lower ends. The coefficient s by which the luminous brightness Bo is multiplied is (1+k)/(1-k).

[0128] Figure 25 (A) is based on Figure 5 , Figure 14 In the case of the backlight device 35B shown, an arithmetic formula for obtaining the light emission amount Boig based on the light emission brightness Bo. Figure 25 The constant s in formula (21) shown in (A) 1 ~s 4 Yes Figure 23 Equation (16) shown in (B), the constant t 1 ~t 4 The attenuation coefficient m can be expressed as Figure 25 (B) Formula (22). When the backlight device 35 is divided into a plurality of regions in both the horizontal direction and the vertical direction, the coefficient s multiplied by the light emission brightness Bo of the region located at the upper and lower ends is 1+k, which is compared with the area sandwiched between the upper and lower ends. The coefficient s multiplied by the luminous brightness Bo of each region is (1+k)/(1-k), and the coefficient t multiplied by the luminous brightness Bo of the regions at the left and right ends is 1+m, which is The coefficient t by which the emission luminance Bo of each of the left and right end regions is multiplied is (1+m)/(1-m).

[0129] In FIG. 21, the data representing the light emission amount Boig output from the light emission amount calculation unit 25 is supplied to the PWM timing generation unit 24 via the white balance adjustment unit 23. The PWM timing generating unit 24 generates PWM timing data that adjusts the pulse width of the pulse width modulation signal generated by the backlight driving unit 36 ​​based on the data indicating the amount of light emission Boig. In this way, in the second embodiment, the backlight driving unit 36 ​​drives the light source 352 in each area according to the amount of light Boig that the light source 352 in each area in the backlight device 35 should emit. Therefore, it can be more accurate than the first embodiment. The emission brightness B of the light that should be emitted from a plurality of areas is controlled.

[0130] In addition, use Figure 23 ~ Figure 25 The described calculation formula for converting the luminous brightness Bo to the luminous amount Boig is an arithmetic expression obtained by approximating the luminous amount Boig as described above, and it is not fully expressed as Figure 22 (B) shows the integrated value of light in the hatched area, but even if it is an approximate calculation formula, the amount of luminescence Boig equivalent to the integrated value of light can be obtained. Furthermore, it is also possible to obtain a more accurate integral value of light by using a complicated calculation formula.

[0131] The third embodiment

[0132] FIG. 26 is a block diagram showing the overall configuration of a liquid crystal display device according to a third embodiment of the present invention. In FIG. 26, the same parts as those in FIG. 1 are denoted by the same reference numerals, and their descriptions are appropriately omitted. In addition, in FIG. 26, for simplification, the non-uniformization processing part 21 in FIG. 1 is omitted, but it may be a structure having the non-uniformization processing part 21 as in the first embodiment. In addition, FIG. 26 has the same light emission amount calculation unit 25 as in the second embodiment, but it may be a structure in which the light emission amount calculation unit 25 is eliminated.

[0133] FIG. 27(A) shows the case where the liquid crystal panel 34 is divided into regions 34a to 34d corresponding to the regions 35a to 35d of the backlight device 35A, showing that the grayscale of the regions 34a, 34b, and 34d is 0 (that is, black) and the region 34c is The maximum gray scale is 255 (that is, white). The luminous brightness B of the light that should be emitted from the regions 35a to 35d of the backlight device 35A at this time is B as shown in FIG. 27(B) 1 , B 2 , B 3 , B 4. At this time, the luminous brightness Bo of the light that should be emitted from the light source 352 itself in the regions 35a to 35d of the backlight device 35A is calculated as Bo as shown in FIG. 27(C) 1 , Bo 2 , Bo 3 , Bo 4 , Becomes a negative value in the regions 35a, 35b, and 35d. In the third embodiment, measures are taken when obtaining the light emission brightness Bo so as not to cause an impossible state in which the light source 352 emits light with a negative brightness value.

[0134] When the backlight device 35 is divided into n areas in the vertical direction, if the light emission brightness of the light source 352 itself in the upper end area is set to Bo 1 , The luminous brightness of the light that should be emitted by the light source 352 itself in the lower end region is set to Bo n , The light emission brightness of the light source 352 itself in each area sandwiched between the upper and lower end portions should be set to Bo i , Then Bo 1 , Bo i , Bo n What becomes negative in calculation is the luminous brightness B of the light that should be emitted from each area 1 , B i , B n meets the Figure 28 (A) in the case of the conditions shown in formula (23). As shown in the formula (23), the calculation condition for the emission luminance Bo to become a negative value is determined by the attenuation coefficient k.

[0135] Therefore, in the third embodiment, the emission brightness B 1 ~B n When the condition shown in formula (23) is met, the luminous brightness B 1 ~B n Corrected to meet Figure 28 After the value of the formula (24) of (B), the emission brightness Bo is obtained. Do not make the luminous brightness Bo become a negative value, at least satisfy Figure 28 The formula (25) of (C) is sufficient. As shown in formula (24), it is allowed to make the gray value of luminous brightness B greater than formula (25), not only because the luminous brightness B is corrected in order to prevent the luminous brightness Bo from becoming a negative value, but also because it can also be visually The luminous brightness B is purposefully increased within a range that does not produce adverse effects.

[0136] Figure 29 The conditions under which the emission luminance Bo becomes a negative value when the backlight device 35 is divided into a plurality of regions in both the horizontal direction and the vertical direction, and the correction value of the emission luminance B are shown. The subscript i marked on the luminous brightness B indicates an arbitrary i-th area in the vertical direction, and j indicates an arbitrary j-th area in the horizontal direction. Figure 29 The formula (26) of (A) expresses the condition of the emission brightness B in which the emission brightness Bo is calculated to be a negative value in a plurality of regions arranged in the vertical direction. When the luminous brightness B meets the condition shown in formula (26), the luminous brightness B is corrected to satisfy Figure 29 (B), (C) Formula (27) or Formula (28) after the value of the luminous brightness Bo is obtained.

[0137] and then, Figure 29 The formula (29) of (D) expresses the condition of the emission brightness B at which the emission brightness Bo becomes a negative value in calculation in a plurality of regions arranged in the horizontal direction. As shown in the formula (29), in the case of the horizontal direction, the condition under which the emission luminance Bo becomes a negative value in calculation is determined by the attenuation coefficient m. When the luminous brightness B meets the condition shown in formula (29), the luminous brightness B is corrected to satisfy Figure 29 After the values ​​of (E) and (F) in formula (30) or formula (31), the luminous brightness Bo is obtained.

[0138] FIG. 27(D) shows the light emission brightness B that corrects the gradation value to the light emission brightness Bo that does not produce the negative value shown in FIG. 27(C). If the emission brightness Bo is obtained using the emission brightness B shown in FIG. 27(D), the emission brightness Bo will not be a negative value as shown in FIG. 27(E). In addition, this is based on Figure 28 In the formula (25) of (C), the light emission brightness B is corrected so that the negative light emission brightness Bo is corrected to the grayscale value 0.

[0139] Returning to FIG. 26, the structure and operation of the third embodiment will be described. In the first embodiment shown in FIG. 1, the image gain calculation section 12 uses the data representing the maximum gray scale of each area of ​​the liquid crystal panel 34 input from the maximum gray scale detection section 11 to obtain the gain, but the gain is shown in FIG. 26 The third embodiment has the following structure. In Figure 26, as in Figure 28 , Figure 29 As described in the above, when the emission brightness Bo is the emission brightness B calculated to be a negative value, the emission brightness B is corrected so that the emission brightness Bo is equal to or greater than the gradation value 0. Then, the emission brightness calculation unit 22 obtains the emission brightness Bo from the corrected emission brightness B, and supplies it to the emission brightness calculation unit 25. The corrected light emission brightness B is supplied to the video gain calculation unit 12. The image gain calculation unit 12 calculates a gain multiplied by the image signal based on the corrected light emission brightness B.

[0140] Regardless of whether the image gain calculation unit 12 uses the data representing the maximum gray scale of the image signal in each area to obtain the gain, or uses the corrected light emission brightness B to obtain the gain, the image gain calculation unit 12 uses the image signal. The value equivalent to the value obtained by dividing the maximum gray scale of the video signal determined by the number of bits by the maximum gray scale of the video signal of each region is obtained as the gain of the video signal of each region.

[0141] In this third embodiment, there is no need to supply data representing the maximum gray scale of each region from the maximum gray scale detection unit 11 to the image gain calculation unit 12. For example, in FIG. 26, the arrow with a dotted line indicates from the maximum gradation detection unit 11 to the image gain calculation unit 12, it is also possible to supply from the maximum gradation detection unit 11 to the image gain calculation unit 12 as in the first embodiment. The maximum gray scale data of the area. Only when the emission luminance Bo becomes a negative value in calculation, the corrected emission luminance B may be used instead of the data representing the maximum gradation to obtain the gain.